The leaves of Serjania erecta Radlk (Sapindaceae) are renowned in ethnobotany for their medicinal properties and are significant as a medicinal resource for traditional Brazilian communities. As necrotic spots are common on these leaves, indicating interaction with phytopathogenic fungi, it was hypothesized that biotrophic fungal species colonize the leaf tissues of S. erecta.
To test this hypothesis, we employed standard techniques in plant anatomy, which enabled us to investigate the interaction of fungal structures with plant tissues and describe the morphoanatomical and histochemical characteristics of the epidermis and limbus of S. erecta.
The anatomical analysis showed the existence of leaf teeth on the leaf tips. Additionally, hyphae, conidiospores, and spores of Bipolaris/Curvularia species were detected on the adaxial epidermis. Moreover, melanized microsclerotia were found in glandular areas of the leaf teeth and the phloem, providing evidence of biotrophic behavior. The hypothesis that biotrophic phytopathogenic fungi interact with S. erecta leaf tissues was confirmed, despite the presence of many bioactive compounds (such as flavonoids, alkaloids, and essential oils), as evidenced by histochemical analyses. The presence of tector, glandular, and scabiform trichomes on the leaf teeth and epidermis was also revealed. This study presents, for the first time, the synthesis of essential oils and alkaloids in the leaves of S. erecta. Additionally, it investigates previously unexplained aspects of the anatomy and histochemistry of the species, as well as its interaction with resident microorganisms. Therefore, it is recommended that future research focus on extracting and characterizing the oils and alkaloids of S. erecta, as well as exploring other aspects related to its microbiome and its relationship.

Secretory trichomes and colleters are two of the secretory structures whose exudates may cover the body of the plant. Such secretions comprise resins or mucilages which are associated with an array of ecological roles. In Rosaceae, secretory trichomes have been reported for the leaves while colleters associated with leaf teeth. Our study aimed to identify the secretory structures of Rosa lucieae and understand the ecological role played by these glands as interpreted by morphoanatomical and histochemical studies. Samples from developing and fully mature leaves were collected, fixed, and processed according to usual techniques for light and scanning electron microscopy. In R. lucieae, colleters are restricted to the leaf and stipular margins and are associated with the teeth. They present a parenchymatous axis surrounded by a secretory palisade epidermis and usually fall off after the secretory activity is finished. Different from colleters, secretory trichomes are persistent. They present a multicellular secretory head and stalk. They are found at the base of the leaflet, petiolule, rachis, and petiole and occasionally on the stipular and leaf margins. The colleters predominantly secrete mucilages while the secretory trichomes secrete lipids and terpenes, both via cuticle rupture. The secretory activity of colleters is predominant in the leaf primordia, holding leaflets together and protecting meristems and leaves from desiccation, while the secretory trichomes maintain their secretory activity at different stages of leaf development, protecting different regions of the leaf against pathogens and herbivores.

Angiosperm leaves present a classic identification problem due to their morphological complexity. Computer-vision algorithms can identify diagnostic regions in images, and heat map outputs illustrate those regions for identification, providing novel insights through visual feedback. We investigate the potential of analyzing leaf heat maps to reveal novel, human-friendly botanical information with applications for extant- and fossil-leaf identification.
We developed a manual scoring system for hotspot locations on published computer-vision heat maps of cleared leaves that showed diagnostic regions for family identification. Heat maps of 3114 cleared leaves of 930 genera in 14 angiosperm families were analyzed. The top-5 and top-1 hotspot regions of highest diagnostic value were scored for 21 leaf locations. The resulting data were viewed using box plots and analyzed using cluster and principal component analyses. We manually identified similar features in fossil leaves to informally demonstrate potential fossil applications.
The method successfully mapped machine strategy using standard botanical language, and distinctive patterns emerged for each family. Hotspots were concentrated on secondary veins (Salicaceae, Myrtaceae, Anacardiaceae), tooth apices (Betulaceae, Rosaceae), and on the little-studied margins of untoothed leaves (Rubiaceae, Annonaceae, Ericaceae). Similar features drove the results from multivariate analyses. The results echo many traditional observations, while also showing that most diagnostic leaf features remain undescribed.
Machine-derived heat maps that initially appear to be dominated by noise can be translated into human-interpretable knowledge, highlighting paths forward for botanists and paleobotanists to discover new diagnostic botanical characters.

Changes of view on the course of the transpiration stream beyond the veins in leaves are followed from the imbibition theory of Sachs, through the (symplastic) endosmotic theory of Pfeffer (which prevailed almost unquestioned until the late 1930s), to Strugger\'s experiments with fluorescent dye tracers and the epifluorescence microscope. This latter work persuaded many to return to the apoplastic-(wall)-path viewpoint, which, despite early and late criticisms that were never rebutted, is still widely held. Tracer experiments of the same kind are still frequently published without consideration of the evidence that they do not reveal the paths of water movement. Experiments on rehydration kinetics of leaves have not produced unequivocal evidence for either path. The detailed destinies of the solutes that reach the leaf in the transpiration stream have received little attention. Consideration of physical principles governing flow and evaporation in a transpiring leaf emphasizes that: (1) Diffusion over interveinal distances at the rates in water will account for substantial solute movement in a few minutes, even in the absence of flow. (2) Diffusion can occur also against opposing now. (3) Volume fluxes in veins are determined by the diameter of the largest leaves examined contain high conductance supply veins which are tapped into by low-conductance distributing veins. (4) Edges and teeth of leaves will be places of especially rapid evaporation, and they often have high-conductance veins leading to them. (5) Solutes in the stream will tend to accumulate at leaf margins. On the basis of recent work, the view is maintained that the water of the stream enters the symplast through cell membranes very close to tracheary elements. Also, that this occurs locally over a small area of membrane. Many solutes in the stream are left outside in the apoplast. This produces regions of high solute concentration in the apoplast and an enrichment of solutes in the stream as it perfuses the leaf. Solutes that enter the symplast are not so easily tracked. Suggestions about where some of them may go can be gained from a fluorescent probe that identifies particular cells (scavenging cells) as having H+ -ATPase porter systems to scrub selected solutes from the stream. Unpublished case-histories are presented which illustrate many aspects of these processes and principles. These are: (1) Maize leaf veins, where the symplastic water path starts at the parenchyma sheath; (2) Lupin veins, where the symplastic path starts at the bundle sheath and where solutes are concentrated in blind terminations; (3) The edges of maize leaves where flow is enhanced by a large vein (open to the apoplast), and solutes are deposited in the apoplast by evaporation; (4) Poplar leaf teeth, which receive strong flows, and where the epithem cells are scavenging cells; (5) Mimosa leaf marginal hairs, which have scavenging cells at their base; (6) Active hydathodes, whose epithem cells are scavenging cells; (7) Pine needle transfusion tissue, which is a site of both solute enrichment (in the tracheids), and scavenging (in the parenchyma); (8) Estimates are made of diffusion coefficients of a solute both along and at right angles to the major diffusive pathway in wheat leaves. The first is 1000 times the second, but is 1/100 of free diffusion in water. Five general themes of the behaviour and organization of the transpiration stream are induced from the facts reviewed. These are: (1) The stream is channelled into courses of graded intensities by the interplay of the physical forces with the anatomical features, each course with a distinct contribution to the processing of the stream. (2) Water enters the symplast at precise locations as close as possible to the tracheary elements. (3) As the stream moves through the leaf its solute concentration is enriched many-fold at predictable sites. (4) Solutes excluded from the symplast diffuse from these sources of high concentration in specially formed wall paths, in precise patterns, at rates which can be measured, and which are low compared with diffusion in water. (5) Other solutes permeate the symplast, often over the surfaces of groups of cells which are organized into recognized structural features. CONTENTS Summary 341 I. What becomes of the transpiration stream ? 342 II. Review 343 III. Preview 355 IV. Overview 361 Acknowledgements 365 References 365.

The proportion of woody dicots with toothed leaves increases toward colder regions, a relationship used to reconstruct past mean annual temperatures. Recent hypotheses explaining this relationship are that (1) leaves in colder regions are thinner, requiring thick veins for support and water supply, with the resulting craspedodromous venation leading to marginal teeth (support-supply hypothesis) or that (2) teeth are associated with the packing of leaf primordia in winter buds (bud-packing hypothesis).
We addressed these hypotheses by examining leaf thickness, number of primordia in buds, growing season length (mean annual temperature, MAT), and other traits in 151 deciduous woody species using georeferenced occurrences and a Bayesian model controlling for phylogeny. We excluded evergreen species because longer leaf life spans correlate with higher leaf mass per area, precluding the detection of independent effects of leaf thickness on leaf-margin type.
The best model predicted toothed leaves with 94% accuracy, with growing season length the strongest predictor. Neither leaf thickness nor number of leaves preformed in buds significantly influenced margin type, rejecting the support-supply and bud-packing hypotheses.
A direct selective benefit of leaf teeth via a carbon gain early in the spring as proposed by Royer and Wilf (2006) would match the strong correlation between toothed species occurrence and short growing season found here using Bayesian hierarchical models. Efforts should be directed to physiological work quantifying seasonal photosynthate production in toothed and nontoothed leaves.